In recent years, a tunnel transistor has been vigorously studied with an aim to achieve higher performance and lower power consumption than a MOSFET. Since the tunnel transistor has a source region and a drain region that are of different conductivity types from each other, a short circuit between a substrate and either the source region or the drain region becomes a problem. Therefore, the tunnel transistor is commonly formed on a semiconductor on insulator (SOI) substrate in order to electrically separate the tunnel transistors from each other. However, since the SOI substrate is more expensive than a bulk semiconductor substrate, a method in which the tunnel transistors can be electrically separated while using the bulk semiconductor substrate is sought after.